The present invention relates to vacuum switches which are designed for use with low direct current voltage electrolytic chemical cells. In such electrolytic chemical cells a very high current level of thousands of amperes are passed through a conductive solution to produce desired chemicals such as chlorine. Many such cells are connected in series and a reliable shunting switch is needed to facilitate bypassing of one or more such cells from the other operative cells for routine maintenance.
The vacuum switch is particularly advantageous for use in the vicinity of such chemical processing equipment with the attendant corrosive atmosphere that is typically present. The electrical contacts of the switch are disposed within the evacuated chamber of the switch and are thus protective from corrosion ensuring their reliable long operating lifetime. An example of a bellows type vacuum switch for such use is seen in U.S. Pat. No. 3,950,628 issued Apr. 13, 1976 and owned by the assignee of the present invention. An improved low voltage vacuum switch designed for such applications is described in copending application Ser. No. 650,322 filed Jan. 19, 1976. In the design described in the copending application, the switch has a very compact profile with corrugated metal diaphram members which permit contact movement while providing a hermetically sealed evacuated device. This copending application also describes the desirability of providing a protective elastomeric insulative member fitted about the switch to protect the thin corrugated metal diaphram walls from the corrosive environment.
Another prior art vacuum switch device is described in West German Pat. 1,218,583, in which one of the contacts is mounted on a support rod extending from a resilient bellows seal. A silicone resin layer is taught on the exterior surface of the flexible or resilient bellows end piece as a protective covering.
In certain electrolytic cell installations, safety requirements dictate that the vacuum switch be fail-safe in the normally open position. Since such vacuum switches are highly evacuated, the atmospheric force acting on the device tends to force the movable contacts together to the closed position. Biasing springs have been used with vacuum switches for biasing them normally open, but such springs are themselves questionable due to the exposure to the corrosive atmosphere associated with the chemical cell.